Noiseless lug tires

Abstract

A noiseless lug tire which runs at a high speed under a heavy load and which satisfies the following conditions. (1) A ratio Wg/Wl is equal to or smaller than 1.0. (2) Each transverse groove for delimiting lugs is not inclined toward an opening of the transverse groove at the kickout side of each lug. (3) Each transverse groove is inclined toward the opening at the stepin side of each lug at an angle of at most 22°. (4) Each portion of a center line of the transverse groove in a substantially total region of a length L of the transverse groove is inclined with respect to the meridian line of the tire at an angle within a range from at most 15° measured in a direction opposite to the inclination direction of the transverse groove as a whole to at most 60° measured in the same direction as the inclination direction of the transverse groove as a whole. (5) Each portion of the center line of the transverse groove in a region extending at least 60% of the length L of the transverse groove is inclined with respect to the meridian line of the tire at an angle within a range from at most 2° measured in the direction opposite to the inclination direction of the transverse groove as a whole to at most 30° measured in the same direction as the inclination direction of the transverse groove as a whole. (6) The inclination of the transverse groove as a whole toward the opening thereof in a region extending from the inner end of each transverse groove to a position which is at least 75% of the length L of the transverse groove and at the stepin side of each lug is increased in response to the advance of tread wear.

What is claimed is: 
     
       1. In a lug tire comprising a number of lugs circumferentially arranged along the periphery of a tread and spaced apart from each other and a number of transverse grooves which are the same in number as said lugs and delimiting said lugs, each of said transverse grooves being opened to only one of two shoulders of the tire and arranged at the left and right sides of the equatorial line of the tire and forming a pair of transverse grooves, each of said transverse grooves having a ratio Wg/Wl of equal to or smaller than 1.0 where Wg is a width of said transverse groove measured at a periphery passing a midpoint between the equatorial line of the tire and the shoulder of the tire and Wl is a width of said lug measured in the same manner as Wg, the improvement comprising; sides of left and right tread halves are divided by said equatorial line which is distant apart from a center line of a road defined by traffic regulations in order to reduce noise to the side of the road closest to the side of the road driven on, each of said transverse grooves as a whole is not inclined toward said opening thereof at a kickout side of each lug, but inclined toward said opening thereof at a stepin side of each lug at an angle of at most 22°, said angle being formed between a segment for connecting two ends of a center line of said transverse groove passing midpoints of widths of said transverse groove measured along the periphery of said tread on the one hand and the meridian line of the tire on the other hand, each portion of said center line of said transverse groove in a substantially total region of a length L of said transverse groove extending along the meridian line of the tire inclined with respect to the meridian line of the tire at an angle within a range from at most 15° measured in a direction opposite to said inclined direction of said transverse groove as a whole to at most 60° measured in the same direction as said inclined direction and each portion of said center line of said transverse groove in a region extending at least 60% of said length L of said transverse groove is inclined with respect to the meridian line of the tire at an angle as defined above and within a range from at most 2° measured in a direction opposite to said inclined direction of said transverse groove as a whole to at most 30° measured in the same direction as said inclined direction, and in a region extending from the inner end of each of said transverse grooves to a position which is at least 75% of the length L of said transverse groove, said inclination of said transverse groove as a whole at the stepin side of each lug toward said opening of each of said transverse grooves is increased in response to the advance of tread wear, the groove center line is inclined away from the direction of advancement to facilitate the escape of air on the side of the vehicle closest to the curb or further from the center line of the road, and a slope is given to groove sidewalls to maintain the escape of air during wear life of the tire. 
     
     
       2. The lug tire according to claim 1, wherein an angle formed between a segment for connecting a crossing point X where the outer contour curve of a tread or its extension line crosses with a transverse groove wall or its extension line to a crossing point Y where an extension line of the transverse groove wall crosses with an extension line of the groove base on the one hand and a normal line drawn perpendicular to the outer contour curve of said tread and passing through said crossing point X on the other hand in a radial sectional plane of said transverse groove at near the midpoint between the equatorial line of the tire and the shoulder thereof and measured at the stepin side of said lug is larger than that measured at the kickout side thereof by at least 8°. 
     
     
       3. The lug tire according to claim 1, wherein said transverse groove wall angle located at near the shoulder and measured at the kickout side of said lug is larger than that measured at the stepin side thereof by at least 4°. 
     
     
       4. The lug tire according to claim 1, wherein said groove wall of said transverse groove located near the shoulder is provided at the kickout side of each lug with a projection having a convex surface facing the groove base. 
     
     
       5. The lug tire according to claim 4, wherein a top point of said projection is vertically spaced apart from the tread surface by a distance which is 20 to 30% of a depth of the transverse groove measured from the tread surface.